In the past, nitrile rubber (acrylonitrile-butadiene copolymer rubber) has been used as a material of rubber parts for automobile use such as hoses and tubes by taking advantage of its oil resistance, mechanical properties, chemical resistance, etc. Further, hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene copolymer rubber) which is obtained by hydrogenating the carbon-carbon double bonds in the polymer main chain of nitrile rubber is further excellent in heat resistance, so is used for rubber parts such as belts, hoses, and diaphragms.
In view of such a situation, Patent Document 1 provides a cross-linkable nitrile rubber composition containing hydrogenated nitrile rubber having α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units, a polyamine-based cross-linking agent, and a basic cross-linking accelerator. Using this composition, cross-linked rubber which is considerably improved in heat resistance and compression set resistance is obtained, but further improvement in compression set resistance has been sought. Further, the above cross-linkable nitrile rubber composition disclosed in the above Patent Document 1 is not necessarily sufficient in processability and scorch stability, so further improvement in the processability and scorch stability has been sought.